Answer:
the time at which P =15 is

the time at which P =20 is

the doubling time

Explanation:
From the information we are being provided with:
The quantity P i.e

In order to determine the time at which P = 15, we have the following:
when P = 15
∴





Hence, the time at which P =15 is

In order to determine the time at which P = 20, we have the following:
when P = 20
∴





Hence, the time at which P =20 is

The doubling time at t = 0, mean P = 2
∴





Hence, the doubling time
